Prior practices of producing a strong metal matrix for iron, cobalt or nickel base alloys generally use a casting technique. In such a technique, as typified by U.S. Pat. No. 3,432,294, the composition control is dictated by the solubilities of the components and this does not permit the precipitation of large volume fractions of individual components into the metal matrix by the casting of the alloy.
In order to increase the volume of a component into the metal matrix beyond those determined by equilibrium considerations, powder metallurgy processes have been utilized. However, in utilizing these techniques, the presence of oxygen in the metal powders, particularly in the form of Cr.sub.2 O.sub.3, and the extremely fine particle size of the dispersed phase have proved problemsome.
Among the prior art metallurgical processes, there is included a process described in U.S. Pat. No. 3,393,067. This patent teaches a process for producing chromium alloy compositions whereby a mixed oxide powder is prepared with carbon and heated to a temperature in the range of 805.degree.-1050.degree.C. whereby any chromium oxide present therein is reduced. The product formed was a fine powder having thoria uniformly dispersed in the alloy matrix. The hydrogen reduction resulted in an oxide content in the final product of less than 0.5 percent, preferably 0.1 percent, exclusive of the oxygen associated with the refractory oxide (ThO.sub.2).
U.S. Pat. No. 3,446,679 discloses a dispersion strengthened nickelchromium alloy. This alloy is first formed by preparing a nickel oxide, chromium oxide and thorium oxide powder. This powder was blended with carbon and heated with hydrogen at 400.degree.C. to reduce the nickel oxide, and then at 925.degree.C. in a H.sub.2 -- CH.sub.4 mixture to reduce the Cr.sub.2 O.sub.3. The product was subsequently treated by known techniques in order to produce a useful alloy foil product.
U.S. Pat. No. 3,595,710 describes a dispersion hardened nickel or cobalt base alloy. A Ni -- Cr -- Fe -- ThO.sub.2 powder was first prepared. The powder was mixed with water and briquetted. The briquettes were hydrogen reduced at temperatures up to 400.degree.C. and finally up to a maximum of 750.degree.C. The briquettes were crushed and pulverized and subsequently subjected to well-known treating operations to produce a dispersion hardened metal product.
The above processes are generally satisfactory in producing dispersion hardened alloys but they do not achieve the strengthening of the metal matrix obtained by the process of this invention which process enables a rather large and controlled amount of carbide particles to be uniformly dispersed in the metal matrix and, at the same time, eliminates the occurrence of the deleteriously high oxygen content which normally would be retained in a product utilizing metal powders as starting materials. Further, by the practice of the process of this invention the mixed powder upon being subjected to high temperature reduction, will not bond together into the form of a sintered hard cake but instead remains as a powder that may be compacted, densified and shaped by normal powder metallurgy methods to yield high strength alloys.
It is an object of this invention to provide a process for pretreating metal powders for the preparation of dispersion hardened alloys. Other objects will be apparent to those skilled-in-the-art from an inspection of the description hereinafter set forth.